I have finally established contact with the reported source of some of the round-nosed external power plugs and cables. Unfortunately, not exactly great news to share, but at least this particular box has been checked off.Mike Haynes up in New Jersey has been holding some New-Old-Stock external power cables. Since they have been in storage, they are probably in better condition than those in service, most of which have deteriorated badly with time. At any rate, apparently these same plugs were used with Enstrom helicopters, and Mike has sold off most of his stock to the helicopter owners. Mike confirmed that there is no known source for new production, and he is not aware of any other NOS cables anywhere.
There are about four of these cables left. If you want one, and you are willing to pay $200 for it, you can contact Mike at 201-343-6787 to order it.
Personally, I continue to recommend that you simply use the drawings on BAC to make (or have made) an adapter plug, which can then be used with standard jumper cables and battery charger connections. These are accessories and do not require any FAA approval.
If there is significant demand for a manufactured adapter plug, I can approach some sources, but we would probably need to commit to at least 100 or 200 plugs to make a production run worthwhile for someone; possibly more. If enough people are willing to sign up for one, I’ll pursue it. I have no clue on cost, but I’m pretty sure it would be far less than than the $200 for the NOS items, and would be far more durable.